Question

Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?

Answer 1

Hint
Electron beam is travelling in a straight line and the magnetic field is coming from the right side. The beam travelling in a straight line will be deflected by the strong magnetic field coming from the right side. The direction of force, current and magnetic field can be obtained by applying Fleming’s left hand rule.

Complete step by step answer
According to Fleming’s left hand rule, if we stretch the forefinger, middle finger and the thumb of the left hand in mutually perpendicular directions. If the direction of the field is represented by the forefinger and the direction of current is represented by the middle finger then the direction of force the conductor will be represented by the thumb on.
We know that the direction of the electron beam is in a straight line from the back wall towards the front wall. The direction of current will be in the opposite direction of the flow of electrons. Therefore the direction of current will be in a straight line from the front wall to the back wall. Since the electron beam has deflected to your right side, the direction of force is towards your right side.
By applying Fleming’s left hand rule, if the thumb represents the force and the middle finger represents the current, then the field will be given by the direction of the forefinger and it will be in a downward direction.
The field will be in a downward direction.

Note
The right hand thumb rule is used to find the direction of magnetic field due to a circular current loop. According to right hand thumb rule, if the direction of the circular current is represented by the direction of the closed fingers of the right hand, then the direction of the magnetic field will be represented by the stretched thumb. All the thumb rules for direction are very important in magnetism.